The current invention relates to processes for the production of polymers. More particularly, the current invention relates to processes for the production of polymers of xcex1-methylstyrene.
Poly xcex1-methylstyrene has many applications including, as processing aids and fusion enhancer/modifiers in applications such as vinyl flooring, as a processing aid in the extrusion and injection molding of PVC piping and profile extrusions such as vinyl siding and windows.
Traditional processes for the polymerization of xcex1-methylstyrene to poly xcex1-methylstyrene have made use of boron trifluoride or other protic acid catalyst/initiators, such as tetrafluorboric acid, hexafluorophosphoric acid and pentafluoroantimonate.
Other work has focused on the use of Lewis acids as coinitiators with cationic carbon species. This work includes: Li et al, xe2x80x9cLiving Carbocationic Polymerization of xcex1-Methylstyrene Using Tin Halides as Coinitiatorsxe2x80x9d, Macromolecules, 1996, 29, 6061-6067; Cotrel et al, xe2x80x9cKinetic Study of the Cationic Polymerization of p-Methoxystyrene Initiated by Trityl Hexachloroantimonatexe2x80x9d, Macromolecules, November-December 1976, vol. 9, No. 6, 931-936; Hotzel et al, xe2x80x9cStudies on Cationic Copolymerization of xcex1-Methylstyrene and Indenexe2x80x9d, Polymer Bulletin 6, 521-527 1982; and Matsuguma et al, xe2x80x9cThe Effect of Counteranions on the Polymer Steric Structure in the Cationic Polymerization of xcex1-Methylstyrenexe2x80x9d, Polymer Journal, vol. 2, No. 3, 353-358, 1971.
A drawback of most current art methods using cationic and Lewis acid initiators is that they require cold temperatures to control the polymerization and obtain polymers of the desired molecular weight and molecular weight distribution. Li et al report in xe2x80x9cLiving Carbocationic Polymerization of xcex1-Methylstyrene Using Tin Halides as Coinitiatorsxe2x80x9d that a rapid and uncontrolled polymerization may lead to side reactions and a broad molecular weight distribution.
A typical industrial process that was run by Amoco utilized boron trifluoride as an initiator to produce poly xcex1-methylstyrene homopolymer. The process was run in a chlorohydrocarbon solvent at xe2x88x9225 to xe2x88x9280xc2x0 C. In addition to the costs introduced by such extreme temperatures, the use of an environmentally unfavorable solvent such as chlorohydrocarbon, which is typical in similar processes, makes this an unattractive process.
Typical anionic catalyst/initiators are alkyl lithiums (U.S. Pat. Nos. 4,614,768, 4,725,654 and 4,748,222) and metal naphthalides, in xe2x80x9cIonic Polymerization of p-Isopropyl-xcex1-Methylstyrenexe2x80x9d, Journal of Macromolecular Sci.-Chem., A11(11), 2087-2112, 1977. Lxc3xa9onard et al.
A drawback of anionic initiators is that they are particularly sensitive to impurities. Unrefined xcex1-methylstyrene, such as what may be obtained directly from an xcex1-methylstyrene manufacturing facility, generally contains a number of trace oxygenated impurities, which adversely affect a number of commonly used polymerization initiators. These impurities include, but are not limited to 3-methyl-2-cyclopentanone (3-MCP), acetophenone, 2-methylbenzofuran (2-MBF) and acetone. In many cases, the presence of these trace impurities has the effect of inhibiting or killing an anionic polymerization initiator, with the result that little or no conversion of the monomer is obtained. As a result, it has been found to be necessary to pre-treat the monomer feed stream, such as with an acidic alumina or via distillation, to remove these trace impurities before proceeding to the polymerization step, adding time and costs to production. U.S. Pat. No. 4,614,768 to Lo, U.S. Pat. No. 4,725,654 to Priddy et al and U.S. Pat. No. 4,748,222 to Malanga disclose the necessity of purifying reactants in processes for polymerizing xcex1-methylstyrene using an organolithium initiator.
Lack of viable alternatives for the production of poly xcex1-methylstyrene homopolymer has led to a lapse in its production and the adoption of alternative co-polymers of xcex1-methylstyrene, such as xcex1-methylstyrene/styrene and xcex1-methylstyrene/vinyltoluene.
Hence, it would be desirable to provide a process for producing polymers of xcex1-methylstyrene that can be efficiently run and controlled at ambient temperatures, does not make use of environmentally unfavorable solvents and consistently produces a polymer of the desired molecular weight. It would further be desirable to provide a process for producing polymers of xcex1-methylstyrene that does not require expensive and time-consuming pre-treatment of the monomer prior to polymerization. The advantages of such a process would include lower costs, a more robust reproducible process, increased efficiency and more controllable process temperature exotherms.
The current invention provides a process for the polymerization of xcex1-methylstyrene that can manageably be carried out at ambient temperature. The current invention also provides a process for the polymerization of xcex1-methylstyrene, which does not require extensive purification of the monomer prior to polymerization.
The invention achieves this through the use of tin IV chloride as an initiator for the polymerization of xcex1-methylstyrene. According to one embodiment of the invention, xcex1-methylstyrene monomer is provided as a solution in an organic solvent, preferably toluene or cumene. A small amount of tin IV chloride is then added to initiate polymerization of the xcex1-methylstyrene. Preferably, the amount of tin IV chloride added is from about 0.10 to about 0.40% by weight based on the weight of xcex1-methylstyrene in solution. The process is run at a temperature greater than about 0xc2x0 C., preferably greater than about 10xc2x0 C., and more preferably greater than about 20xc2x0 C. The initiator may be added either neat or as a solution in a suitable solvent. Preferably, the initiator is added in a suitable solvent. The process may be run as a batch process or in continuous production.
According to one embodiment, the process may be run with xcex1-methylstyrene and one or more co-monomers including, but not limited to propylene, ethylene, styrene, butadiene, acrylonitrile and methylmethacrylate to produce an xcex1-methylstyrene co-polymer.
The process according to the current invention uses tin IV chloride as an initiator for the polymerization of xcex1-methylstyrene to produce a poly xcex1-methylstyrene polymer. It has been discovered that the use of tin IV chloride as an initiator for the polymerization of xcex1-methylstyrene eliminates the need for tedious and expensive purification of the monomer prior to the polymerization. Additionally, it has been discovered that using tin IV chloride as an initiator, the polymerization can be initiated at ambient or higher temperatures without resulting in uncontrolled polymerization.
Examples 1 through 4 and the data in Tables I through IV demonstrate the superiority of the inventive process using tin IV chloride as a polymerization initiator.